const arr: number[] = [1, 2, 3]
const set: Set<number> = new Set([3, 4, 5])
const map: Map<number, number> = new Map()
map.set(1, 3)
map.set(2, 5)

for (let item in arr) {
  console.log(item) // 0 1 2
}
for (let item of arr) {
  console.log(item) // 1 2 3
}